Head lice 'are becoming indestructible'

You can comb them out, zap them with chemicals or simply keep scratching. But head lice have a habit of maintaining a firm grip on their habitat.

And the bad news is they are becoming increasingly resistant to the most common treatments.

Scientists believe that 80 per cent of the bugs are immune to over-the-counter lotions. They found lice were untroubled by the chemicals permathrin and phenothrin, found in popular bug-busting brands such as Lyclear and Full Marks.

The experts say the process of natural selection means the insects have developed a resistance to the lotions. The findings will not just

leave children, parents and teachers scratching their heads. It will almost certainly start a scramble to discover a lotion to do the job better.

Lucrative

Eliminating head lice is a lucrative business, with Britons spending £30million a year on treatments.

Scientists at the Communicable Disease Surveillance Centre in Cardiff discovered four out of five lice were resistant to the chemicals.

A team led by Dr Daniel Thomas armed themselves with nit combs to visit 31 schools in Wales.

Eight per cent of children tested had head lice and researchers managed to remove 4,000 nits - head lice eggs - from itchy heads. Each nit collected was tested for resistance to pyrethroids, which are used in the most popular treatments for lice.

They require a shorter application time and do not smell as strongly as other chemicals. More than 80 per cent of the lice were resistant to the insecticides which are designed to attack the insect's nervous system, the scientists discovered.

This was because of the process of natural selection, said Dr Thomas. Most lice have developed a gene which makes them more resistant to poisons following years of exposure to the chemicals.

Insects either develop ways of counteracting the chemicals before they affect their bodies or they become less sensitive to them, said Dr Thomas, whose findings are published in the journal Archives of Disease In Childhood.

He said there was no reason to suppose the findings would not be replicated across the rest of Britain.

Head lice live close to the scalp, where there is guaranteed warmth, food and shelter. They cannot fly, jump or hop and are spread when people's heads touch each other.

Last year a study found those who fine-combed their wet hair were four times more likely to remove head lice than those relying on products bought at the chemist.